1. Field of the Invention
Recently, in the field of display devices that perform image display, flat type display devices formed by disposing pixels (pixel circuits) including light emitting elements in a matrix form have been spreading rapidly. As the flat type display devices, organic EL display devices using organic EL (electroluminescence) elements that utilize a phenomenon of light emission at the time of applying an electric field, for example, to an organic thin film have been developed and commercialized.
2. Description of the Related Art
The organic EL display device has the following features. The organic EL element can be driven by an application voltage of 10 V or less, and thus has low power consumption. In addition, since the organic EL element is a self-luminous element, the organic EL display does not need a light source (back light) that may be essential to a liquid crystal display device. In addition, the response speed of the organic EL element is very high with response time of several microseconds, and accordingly, no afterimage occurs at the time of displaying a motion picture.
Similarly to the liquid crystal display device, a simple (passive) matrix type or an active matrix type may be used as a driving method of the organic EL display device. Recently, active matrix-type display devices in which an active element such as an insulated gate-type field effect transistor (generally, TFT (thin film transistor)) is disposed in a pixel circuit have been actively developed.
It is generally known that the I-V characteristics (current-voltage characteristics) of the organic EL element degrade as time elapses (so-called degradation overtime). In addition, a threshold voltage Vth of a driving transistor or the mobility μ of a semiconductor thin film that configures a channel of the driving transistor (hereinafter, described as “mobility of a driving transistor”) changes over time or may be different for each pixel due to a deviation in the manufacturing process thereof.
Accordingly, in order to maintain emission luminance of the organic EL element to be constant without being affected by the above-described factors, a configuration in which a compensation function for characteristic variances in the organic EL element and correction functions including a correction function for variances in the threshold voltage Vth of the driving transistor (hereinafter, described as “threshold value correction”) or a correction function for variances in the mobility μ of the driving transistor are included in each pixel circuit has been used (for example, see JP-A-2006-133542).